A shaped sceptre is best, with 'Gain 20% of Elemental Damage as Extra Chaos Damage', but any good spellcaster sceptre is fine. Doriyani's Catalyst is the budget choice for this build.

Shield

Get a spellcaster shield with extra block chance if possible.

Armour

6 Linked Inpulsa's Broken Heart is what we want. A rare chest would also be viable, but the chain explosions are a great source of clearspeed, so Inpulsa's is recommended. For advanced DPS purposes, you can take advantage of the corruptions '+1 gems' and '+2 duration gems' - +2 duration gems ONLY works if you are using Vaal Arc because regular Arc does not have a duration tag. That being said, +2 to Arc gives an almost 20% damage boost, so it's very well worth the cost if you have the money.

Rings

Call of the Brotherhood allows us to convert 40% of our Arc damage into cold damage, which allows us to chill and freeze enemies, especially with our focus on crits.

Berek's Grip is synergistic with Call of the Brotherhood, and it provides life leech, for some additional survivability. Getting life leech on elemental builds is difficult, so Berek's Grip definitely helps.

Neither ring needs to be corrupted - it's hard to cap resistances with corrupted rings, but it's definitely a source of hidden power in the build if you can get Wrath corruptions.

Amulet

High life and damage, particularly crit multi if available. The Incursion Temple mod '.4% of Lightning Damage Leeched as Life' will allow you to possibly drop Berek's Grip, if you can find an otherwise suitable amulet.

Helmet

A rare helmet with an Arc enchant is great, though there are many options.

Gloves

We want gloves that have an effective extra link for our Lightning Spire Trap setup.

Boots

30% movement speed and a fat dex roll are what you're looking for here.

Belt

Get a Stygian with life and resistances. Movement speed prefix is nice but not necessary.

My Arc setup uses Empower 4, but there are other good options such as Increased Critical Damage. Vaal Arc is situationally good, but priority is a level 21 Arc.

Lightning Spire Trap

Lightning Spire Trap is our non-reflectable single target skill - three traps melt most bosses, including split-phase Uber Atziri. Supported in our gloves with Trap and Mine Damage as well for an effective 5-link.

Auras

We swap Herald of Thunder for various purities as necessary for very-tough content, such as Uber Atziri.

Movement Skill

Since we are a sceptre build, we get to use Shield Charge!

CWDT #1

A standard low-level Cast When Damage Taken setup

CWDT #2

A second, high-level Cast When Damage Taken setup - you can experiment here with your own ideas.

Build Costs and Thoughts

Spoiler

My version of this build costs around 50 exalts. It's tremendously versatile - it can clear everything in the game, save for possibly Uber Elder and Hall of Grandmasters. It's Shaper-viable at a much lower gear level as well - you can comfortably kill Shaper at half of my power level, for instance.

There are plenty of arc builds available right now, many focusing on traps and totems - those are fine builds and likely even stronger than self-casting Arc, but that doesn't mean that self-casting isn't both viable and very fun. In addition, this build incorporates a lot of good gearing ideas that can be incorporated into other Arc builds as well, many of which use things like Essence Worm and Mind over Matter.

Nice build- I’m running something very similar to you this league and have absolutely loved it so far- the clear speed in my configuration is amazing and still has a lot of room to improve. Am also running T15/T16s no problem with a lot of magic find gear to improve map returns. I’d like to make some suggestions, however, as I think there are a variety of quality of life improvements that you can make to make the build shine even more.

Items:
Essence of insanity crafted gloves: this is the #1 quality of life improvement you can make to your shield charge. Your links should be shield charge, culling strike (for 10% more attack speed as well as boss killing), faster attacks, and fortify on the gloves. The trap setup in your current gloves is a little too cute for me, you don’t really need it for boss damage if the rest of your gear is good.

2 Socket lightpoacher: Not only is lightpoacher going to give you an additional ~10% dps because of the two sockets, but I can’t emphasize how huge of a quality of life boost it is to have the instant heals from the charges you expend. Aside from a bereks grip, which in general is a pretty mediocre unique ring, there aren’t many ways for us to leech or gain life back, so lightpoacher is a really nice quality of life improvement overall.

Headhunter: I know it’s not cheap (I’m currently on 5 doctors, working towards getting mine), but there is basically no other belt we should be using for this build other than headhunter so long as you can afford it- other than life, resistances, a socket, and an insignificant amount of movement speed, our belt slot really can’t provide us with much- the buffs you get on headhunter scale extremely well with this build as it’s self cast and shield charge will get ridiculously fast. The dexterity alone on it is going to let you use haste/vaal haste in the end which is absolutely insane if you’ve already stacked proper attack speed on your gear. My ideal two aura setup would be an level 4 enlighten linked to wrath and haste. You’re also going to probably need to pick up some mana reservation in the top left of the tree to do this. To give you an idea, haste is comparable to herald of lightning in terms of dps, but getting vaal haste for free makes the dps jump way over what herald of lightning has to offer. That and you also get a huge quality of life/clear speed improvement because of the attack speed gains from haste and vaal haste.

Jewelry slots: you can get more dps with this build by using a mark of the shaper and a well crafted elder ring over call of the brotherhood/ berek’s grip. Using this ring with the aforementioned pieces of gear, however, will make it very difficult to cap resistances- you’re going to have to have a really good shield, amulet, boots, gloves, and other ring to make mark of the shaper work. Well crafted lightning % opals are another option that I currently use for bossing. For amulet slot- life, multi, spell damage are obviously important, but you can also craft a shaped amulet with the lightning damage leeched as life % which is huge for us. Given that there aren’t that many great prefixes for us anyway, this line is definitely worth going for.
Anyway, my build is still a work and progress and my links and boot enchantment are crap atm, but I’ll post an update with gearing once I’m finished with my take on self cast arc inquis. Take a look at my profile if you’re interested

Nice build- I’m running something very similar to you this league and have absolutely loved it so far...

Thanks for the ideas. Here are my thoughts.

I am very sold on Lightning Spire Trap for the build - it is a huge damage increase, and it enables us to run Atziri and Uber Atziri. That being said, you can run it in a shaped helmet, so you could run Insanity gloves if a good pair was available.

I like the idea of Lightpoacher - I really don't love Berek's Grip, so going Lightpoacher could solve some problems. We have extra sockets too, so no huge loss there. I might do some experimenting - I typically optimize around end-game boss experiences, so whichever works best on the top-end content would be the one I'm interested in.

I also like Mark of the Shaper, but I think Call of the Brotherhood is a defining item for this build and don't see dropping it. I did see an Elder CotB up for 4ex at one point and almost bought it. I ran the numbers, tho, and Mark of the Shaper is not as big a damage increase over Berek's as you would expect (when you are using CotB), so I said no to it.

I agree that Headhunter is a nice addition, just not in my budget.

I like your ideas on amulets. Ultimately, it's a slot where getting the right item is both pricey and may not be available at all times.

Wanted to share my progress with my similar version of this build. Have managed to make a lot of currency this league, and have been able to push my bossing gear up to 1.9 million shaper dps (with power charges and other buffs you would get off shaper, but without frenzy charges or onslaught). With frenzys and onslaught, the number goes to 2.3 million shaper dps.

Anyway- here's the gear:

The +2 to duration of socketed spells in the chest is about a 10-11% dps increased with decent gear. It's better than +1 socketed gems because arc scales so with levels. Still need to slam a bunch of jewels and try to go for good 4-mods, but will focus on that later. Also still need to essence craft a good weapon with the extra chaos damage- overall things are coming together though- I could see this build hitting 3 million shaper dps with absolutely godlike gear.

I also want to say that this is only for bossing, for regular mapping, I'm using the following for increased returns. Can very comfortably farm T16s and even some of the guardians with MF gear on.

This is pretty nice gear - I definitely would like to take your build for a spin to check the differences, but obviously PoE doesn't let us do such things. Very nice corruption on the Inpulsa's - mine only went all-white, unfortunately, and I don't have the bankroll to afford a better one. You actually NEED a Vaal Arc for +2 duration because regular Arc doesn't have a duration tag, which is pretty funny.